Those bonuses that specifically state that you can play Keno while the bonus is in play are listed here.
It may not always be stated clearly in the terms however, as some casinos like to mention the games that specifically cannot be played while a bonus is in play, rather than list those games that are permitted to be played. Therefore, if you would like to play keno while clearing a bonus, and the bonus you had in mind to go for is not listed here, you should still check directly with the casino support staff just in case it is permitted.
One good thing about this kind of game will be the jackpot bonuses, which can be worth playing for.
Also, it should be noted that just because a game is termed as a scratch card game, does not mean that it will bear much resemblance to other games at other casinos that are also called scratch card games.
Essentially though the premise behind the games will be the same, but the format can and does vary wildly.
As ever, the bonuses listed here specifically include this game type in their terms.
There is not much strategy to be employed with these games; that can be a lot of the fun of them of course, they are pure gambling games. With the added prospect of a jackpot win, I can see why they are growing so popular.